This invention generally relates to electric incandescent lamps and has particular reference to an improved filament mount and seal-embedded electrical juncture for an incandescent lamp of the halogen-cycle type, and to a method of manufacturing electric lamps having such mount assemblies and electrical junctures.
Halogen-cycle incandescent lamps are well known in the art and utilize a halogen, such as bromine or iodine, within the envelope which returns vaporized tungsten material to the filament and thus prevents the envelope walls from progressively blackening and drastically reducing the light output of the lamp during its useful life. Due to the high bulb-wall temperatures involved and the use of a halogen-containing atmosphere, the lamp envelope is made from quartz or a hard glass (such as borosilicate or aluminosilicate glass) that has a high melting point. In order to insure the integrity of the hermetic seal which joins the envelope to the lead-in conductors, the standard practice in the prior art was to connect the outer lead wires to the ends of the tungsten filament (or to a pair of inner lead wires) with ribbon-like conductors such as molybdenum foil or the like that are embedded in the fused mass of quartz or glass which comprises the sealed end of the lamp envelope. A tungsten-halogen incandescent lamp which employs both of the foregoing structural arrangements is disclosed in FIGS. 1-4 of U.S. Pat. No. 3,588,315, issued June 18, 1971 to Levand, Jr. et al. A halogen incandescent lamp having a filament with legs of coiled tungsten wire that are connected to ribbon conductors and partly embedded in the envelope seal is disclosed in U.S. Pat. No. 3,668,391 to Kimball. It is also well known in the art to connect the coiled filament of a compact halogen-cycle incandescent lamp to the outer lead wires by flattening the seal-embedded ends of the latter and joining them to inner lead wire components that are secured to the legs of the filament coil. A halogen-cycle incandescent lamp constructed in this manner is disclosed in U.S. Pat. No. 3,445,713, issued May 20, 1969 to Cardwell, Jr.
A tungsten-halogen type incandescent lamp having an envelope that is composed of hard glass (such as aluminosilicate glass) instead of quartz and which employs a pair of one-piece lead-in wires that extend from the coiled filament through and beyond the press-sealed end of the envelope is described in U.S. Pat. No. 3,829,729, issued Aug. 13, 1974 to Westlund, Jr. et al. This patent also discloses that U.S. Pat. No. 3,641,386 to Audesse et al. describes a halogen incandescent lamp that employs a borosilicate glass envelope. U.S. Pat. No. 3,648,094 to DeCaro et al. also discloses a halogen-cycle lamp that has a borosilicate glass envelope.
U.S. Pat. No. 3,544,830 to George et al. discloses a method of making a filament-mount assembly for a quartz-halogen lamp using a U-shaped lead-wire support member and a pair of ribbon conductors that are subsequently embedded in the press-sealed end of the envelope after the U-shaped support member is severed.
Since the electrical junctures between the lead-in wires and the filament of such incandescent lamps are crucial in view of the fact that they obviously will render the lamp inoperative if the junctures fail, it is important that such junctures be made as strong and as reliable as possible. This is especially important in the case of compact halogen-cycle type incandescent lamps that are used as the inner light sources in sealed-beam headlamps insofar as such lamps are inherently subjected to severe rough service conditions when the headlamp is in use on the motor vehicle.
It would accordingly be very desirable to provide a simple but very reliable arrangement for electrically connecting the filament of a compact incandescent lamp with the lead-in conductors which not only improves the lamp quality but facilitates manufacture of the lamp and reduces its cost, and to effect the electrical junctures in such a manner that the filament mount and its electrical connections are rugged enough to withstand the mechanical shocks and vibrations encountered during the life of the lamp.